The AMD Zen Architecture explained

Both AMD and Intel release new processors nearly every year. Intel released their Skylake processors a year ago and is getting ready to release the new Kaby Lake processors. Similarly, AMD released their Excavator processors last year. Now they’re getting ready to release new processors based on the Zen architecture.

What is a processor architecture?

A processor architecture (or microarchitecture) is how a processor handles a set of directions given to it. In general, all processors run through the following steps, called the instruction cycle:

Read and decide an instruction

Locate any data needed to process the instruction

Process the instruction

Output the results

The processors contain a lot of different units, each responsible for different functions, like Integer Units, Floating Point units, Cache units, Power Management units, data fetching units, etc. A microarchitecture puts all of these things together and tries to optimize for performance, power, cost and other considerations.

What is the AMD Zen architecture?

The Zen architecture is AMD’s first completely new architecture since they released the Bulldozer architecture in 2011. Since then they’ve released improvements to the Bulldozer architecture including the Piledriver, Steamroller, and Excavator families of processors.

Five years ago, AMD emphasized multi-core CPU performance, while Intel concentrated on high frequency single core performance. For example, if you compare the similarly priced Intel Core i7-6700K and AMD FX-9590 processors, the FX-9590 has eight cores while the i7-6700K has four. However, if you look at single core performance, the i7-6700K is faster than the FX-9590. As any dedicated gamer can tell you, modern games (and other software) just aren’t optimized for multi-threaded processors, and instead the focus remains on fast single-core performance. New graphics APIs like DirectX 12 and Vulkan are supposed to address that.

This means that currently, AMD processors have lower performance in games and other applications when compared to similarly-priced Intel processors. The new Zen architecture aims at addressing this by improving single core speeds while continuing to support multi-core performance.

Geeky Details

AMD’s goal of a 40% increase in instructions per clock compared to their previous generation of processors was achieved through three main approaches: better core design, improved cache, and a focus on lower power (a.k.a. increased efficiency).

The improvements in core engine come from things like larger ques for retiring, loading and storing, larger instruction schedulers, and better branch prediction. Another big improvement is from SMT, or simultaneous multithreading, similar to Intel’s HyperThreading. The Zen architecture is “wider” – it can accept more instructions per cycle, 6 compared to 4. A deep learning approach allows the Zen architecture to look further into its queue of tasks to complete and pick off the ones in can execute in parallel.

A low latency, high bandwidth cache system allows the processor to store and access data more quickly.

The new 14nm FinFet technology already used in AMD’s Polaris graphics cards allows the Zen processors to be more efficient, using less power. The increased efficiency comes from a reduction in TDP (Thermal Design Power), which is a measure of how much power (in Watts) a processor will draw, and also an indication of how hot it will get. Reportedly, the Zen processors will have a TDP of 65W for quad-core CPUs and 95W for the eight-core CPUS. Compare that with the 91W TDP of the quad-core Intel i7 and 140W for the eight core version. The AMD FX-9590 has a TDP of 220W, which lead to many jokes about AMD processors running hot.

New AM4 Socket

The new Zen processors will need new motherboards with the AM4 socket. This will be the first socket that supports DDR4 memory. It will also unify the AMD sockets: currently high end CPUs use the AM3+ socket while lower end APUs use various other sockets like the FM2+.

An APU is an Accelerated Processing Unit, which is AMD’s way of separated processors with integrated graphics. The new Zen APUs will feature the same Polaris GPU architecture found on AMD’s new graphics cards, like the RX 480.

Specs are one thing, but real-world performance is another. Will this generation of processors finally be enough to level the playing field between AMD and Intel? Only time will tell. Details are still murky, but AMD Zen processors will be officially released in early 2017, most likely at CES in January. Other rumors suggest Zen chips will arrive in October. It will be interesting to see if AMD can finally make a comeback in the gaming PC market.